Experimental and numerical responses of fibroblast and epithelial cells to the frequency of electric toothbrush.

In the oral environment, fibroblast and gingival epithelial cells undergo distinct forces. Chewing, brushing, or force interactions with dental materials like implants can produce these forces. The behavior and response of these cells to forces are determined by their stiffness. Additionally, this behavior can be crucial in mechanosensory and tissue development. In this study, after being cultured using nanomagnet materials, fibroblast and epithelial cells were subjected to magnetic tweezers cytometry testing, and the viscoelastic model was used to determine their stiffness. The reaction of single gingival cells was modeled by determining the stiffness of cells at Gel Point frequencies and the operating frequency of electric toothbrushes and employing the Finite Element Method (FEM). Epithelial cell and fibroblast gel points took place at frequencies of 5Hz and 3Hz, respectively. At these frequencies, the behavior of cells is both quasi-solid and fluid. In addition, the findings of the finite element analysis demonstrated that the cells undergo a greater degree of deformation at the Gel point frequency compared to the operating frequency of toothbrushes. This quantity was approximately 331 times greater in epithelial cells, which reached a maximum of 7.114 µm. Additionally, the maximal fibroblast cell deformation at 3Hz frequency was determined to be 2.981 µm, which is roughly 117 times that at 150Hz frequency.

Relaxation and creep response of the alveolar lung to diagnosis and treatments for respiratory and lung disorders.

BACKGROUND: The lung Extracellular Matrix (ECM) contains a considerable part of the parenchymal cells. It contains three essential components: elastin and collagen within a proteoglycan (PG) viscoelastic network. Elastin provides the lung's elasticity property, a necessity for normal breathing, while collagen prepares structural support and strength, and PGs give stability and cushioning within tissue loading. Bacterial and viral respiratory diseases are dependent on changes in the ECM ingredients, which result in an alteration of the lung tissue strength. PURPOSE: In the present study, this variation was investigated by changing the volume ratio of the ECM ingredients in the viscoelastic model. RESULTS: As a result, the relaxation curves continuously declined by reducing the volume ratios of elastin, collagen, and PGs; subsequently, the lung stiffness decreased. Also, the Standard Linear Solid (SLS) model-based results demonstrated excellent accordance with empirical data with only minor deviations. The resting relaxation modulus and the creep modulus for the ECM tissue were 51 kPa and approximately 0.02 kPa, respectively, and the maximum total modulus of elasticity reached 121 kPa. CONCLUSIONS: Moreover, this model demonstrates individual alveolar mechanical behaviours and adds another pathway to the generalized Kelvin-Voigt and Maxwell models in predicting the progress of lung diseases.

Experimental tracking and numerical mapping of novel coronavirus micro-droplet deposition through nasal inhalation in the human respiratory system.

It is essential to study the viral droplet's uptake in the human respiratory system to better control, prevent, and treat diseases. Micro-droplets can easily pass through ordinary respiratory masks. Therefore, the SARS-COV-2 transmit easily in conversation with a regular mask with 'silent spreaders' in the most physiological way of breathing through the nose, indoor and at rest condition. The results showed that the amount of deposited micro-droplets in the olfactory epithelium area is low. Also, due to receptors and long droplet residence time in this region, the possibility of absorption increases in the cribriform plate. This phenomenon eventually could lead to brain lesion damage and, in some cases, leads to stroke. In all inlet flow rates lower than 30 L/min inlet boundary conditions, the average percentage of viral contamination for upper respiratory tract is always less than 50% and more than 50% for the lungs. At 6L/min and 15L/min flow rates, the average percentage of lung contamination increases to more than 87%, which due to the presence of the Coronavirus receptor in the lungs, the involvement of the lungs increases significantly. This study's other achievements include the inverse relationship between droplets deposition efficiency in some parts of the upper airway, which have the most deformation in the tract. Also, the increased deformities per minute applied to the trachea and nasal cavity, which is 1.5 times more than usual, could lead to chest and head bothers.

In silico investigation of sneezing in a full real human upper airway using computational fluid dynamics method.

BACKGROUND AND OBJECTIVE: Sneezing is one of the most critical conditions that can occur in the human upper airway. As some reports confirm the injury to the human upper respiratory airway while sneezing. Therefore, the accurate study of the distribution of pressure and velocity in this case is of great importance. METHODS: In the present study, using a real human upper airway model, the pressure and velocity of the airflow generated in the tract during the sneezing have been investigated. Also, considering the results from a spirometer device as a boundary condition in the simulation process, the calculations have become reliable. RESULTS: According to the results, during sneezing, taking into account that the average outlet flow rate from the mouth is 4.79 L/s, the velocity of outlet airflow from the mouth and nose reaches 5.3 and 8.4 m/s, respectively. These values were 11.5 and 19, respectively, when the desired maximum flow rate was 10.58 L/s. It can be concluded that the increasing of trachea flow rate, leads to higher percentage of the outlet flow rate from the nose . The highest average pressure and velocity have been occurred in the trachea. Among other salient results of this report, increased average static pressure of larynx to approximately 10 kPa can be pointed which indicates that this area is critical so that the thyroid cartilage defect is likely to occur. It is also noteworthy that the increase of speed at nasopharynx is up to 125 m/s so that the cross-section changing in this area leads the fluid acts as a jet flow. Due to the specific geometry of the nasal cavity, some streams similar to poor shocks are formed, these shocks get stronger by increasing of the flow rate. The thyroid cartilage and nasal cavity are exposed to maximum static pressure extremums, respectively. CONCLUSIONS: We introduced a model simulating a normal sneezing for two cases using a healthy 30-year-old male person. We believe that the model should be applied for different persons and an atlas of data could be obtained from different cases. This may help the medical system to have more data about the sneezing process.